Passive fences have been used to stop wind-borne transport across dessert terrain. However after a period of time, passive fences become full of sand and their barrier efficiency drops to zero. Other prior art solutions to the problem of wind-borne sand and snow include vertical extension of the existing fence, building a new fence at a different location, and removal of accumulated particles from the base and downwind shadow area of the fence line.
Other approaches to halting or slowing sand drift include planting sand vegetation and sand stabilization using chemical agents, e.g., crude oil. However, vegetation is difficult to maintain in desert and arid lands having harsh environments. Chemical agents can also present potential danger to the under ground water supply and to animals and plants. Application of crude oil to the surface of the sand suppresses vegetation and has a limited useful term, especially if the area is destabilized by animal movement and/or transportation systems.
Sand or snow barriers having movable surfaces responsive to the direction and/or velocity of the airborne particles have been disclosed in the prior art. For example, U.S. Pat. No. 4,549,724 describes a self-orienting barrier fence that moves to maintain its slated surface perpendicular to the prevailing wind.
Protective fencing formed of a plurality of horizontally arranged slats or vanes that are upwardly curved and pivotally mounted along the horizontal axis are disclosed in U.S. Pat. No. 3,473,786. The horizontal vanes are attached to a fixed frame and respond to changes in the angle of attack of the wind to provide the maximum lift to the air stream containing the particles to carrying the particles over a roadway or other right-of-way, rather than cause them to fall at or downwind of the device.
A snow fence having a rotatably-mounted plate mounted on a fixed base is described in U.S. Pat. No. 6,053,479 as a passive snow removal system, using a triangular plate to create vortices in a downwind area that scour the ground and prevent accumulation and drifting.
As will be apparent to one of ordinary skill in the art, the prior art barriers or fences provided with movable assemblies are also vulnerable to sand or snow accumulation around their stationary supports which can eventually render them partially or wholly inoperable.
I have invented an apparatus which performs as a sand fence and at the same time will adjust its position to maintain the operative portions above the top of the sand dune accumulated thereby. In particular, the present invention relates to a dynamic sand or snow fence or break that moves vertically upward as sand accumulates therebeneath to maintain its fully-operable position above the surface of the accumulating sand particles at its base.
The dynamic sand barrier or break is highly efficient in removing airborne particles carried along the earth's surface in order to protect downwind terrain and facilities from sand advancement and drifting. It also provides a self-positioning and self-orienting sand barrier whose power requirements are met by the actual wind that is driving the particles for which it serves as a barrier.